Are lone sociable dolphins mentally ill?

Are lone sociable dolphins mentally ill?

Apparently most injuries to humans by wild dolphins are inflicted by lone sociable (to humans) dolphins. I think males sometimes strike out on their own, but in this case is it possible that lone sociable dolphins have been ostracized from their pods due to mental illness?

Lone individuals occur in many mammal populations without the lone animal being “abnormal”. Lone dolphins could be alone for a number of factors, but being mentally ill is not the main hypothesis as dolphins are very social and some individuals may occur naturally that do not prefer large social groups.

  1. A dolphin might leave the pod for a short period of time to heal from an injury or get well from a physical illness
  2. A dolphin may live alone for periods of time when it does not want to be involved in the consequences of group living
  3. Food availability & prey selection (less food, better to be alone or prefers to eat a specific type of food not located near the main pod)
  4. Fewer predators (do not need the protection of a pod) in the current habitat - most lone dolphins are observed in coastal habitats, whereas when found in the open ocean lone dolphins will swim with other species of cetaceans
  5. Overall decrease of a larger population leading to many smaller groups with lone individuals spending longer periods “alone” as they seek out a new group to join
  6. Reproduction and social structure - some males dolphin species are more solitary when females are frequent in the area, genetic mixing (males/females leave pods for new pods)
  7. Loss of entire pod or old age

There are many other factors for why lone dolphins occur, but I don’t think we should discount human interaction either. Lone dolphins that occur inshore have interacted with humans before, enough that their social behaviours are directed towards the humans. There is some pretty interesting research on lone dolphins and humans!

Merritt Adkins, Degree in Marine Biology, Master's in Environmental Science